This invention relates to pitch-based carbon fibers having superior properties useful for fabrics or non-woven fabrics.
The pitch-based carbon fibers having peculiar twists or twists and curls of the present invention give bulkiness which has not been given by conventional carbon fibers and the non-woven fabrics produced therefrom show superior shape-retaining property, dimensional stability, heat-retaining property and cushioning property.
The pitch-based carbon fibers of the present invention give superior shrinking property, shock absorbing property, heat-retaining property and cushioning property to thread or spun yarn.
Irrespective of natural fibers or artificial fibers, most of fibers useful as raw materials for clothes have twists and curls. It is considered that such a form has a function of improving workability of fibers and has a capability of holding air-containing space. But most of fibers for industrial purpose have a straight form without curls.
Particularly in case of carbon fibers, those which have no twist or curl have been prepared. The reason for this matter is as follows. At the time of production of carbon fibers from fibers of an organic high molecular substance, carbonization treatment is carried out usually under stretching in order to make their strength greater. And by the stretching applied for a long time, strain inherently possessed by the fibers of the organic high molecular substance is lost. On the other hand, since plastic deformation temperature of carbon is higher, designing of facilities for providing secondarily twist or curl is difficult.
Further, in case of pitch-based carbon fibers, the carbonization under stretching is unnecessary. But since precursor fibers have extremely low strength, it is considered that forming twist and curl by providing strain onto the fibers is an intolerable process for the fibers. On this account, in the quality evaluation standard of pitch fibers, there seems to be such a tendency that if a deformation suggesting of the existence of such a strain is not found, quality is regarded to be good.
However, when extensive industrial materials are taken into consideration as use for carbon fibers, it is not a clear-cut point of view that straight yarn is most preferable as in case of the use in fiber composite materials. It is considered that there is naturally a case where non-straight fibers or yarn are preferable if materials of such a shape as non-woven fabrics, spun yarn fabrics or the like are taken into consideration.
It is an object of the present invention to overcome the problem of conventional carbon fibers which are greatly inferior to other artificial fibers in processability due to their straight shape having no twist or curl.